A critical analysis of the growth in length of the cranial base.

The basicranium chondrifies and ossifies in a posteroanterior, but ceases growth in an anteroposterior sequence. The synchondroses respond to "built-in" and local influences, show symmetric or asymmetric bipolar growth and cease growth long before synostosis. Individual variations in amount of bone formation occur in them within an overall species pattern. The ethmoid stops elongating early in man and rhesus monkey, but grows until maturity, although least of all the basicranial bones, in other animals. The hypophyseal fossa drifts significantly caudally.